#!/bin/python

import sys

def height(h, word):
    char_h = [h[ord(c) - 97] for c in word]
    return max(char_h)

def width(word):
    return len(word)

h = map(int,raw_input().strip().split(' '))
word = raw_input().strip()

print(width(word) * height(h, word))